In recent years , reduction of vehicle exterior noise and silencing in vehicle compartment have been progressing and engine noise has been reducing; and accordingly, noise of a vehicle AC generator serving as an auxiliary machine that rotates in a relatively high speed has been regarded as more problematic than ever before.
As one of countermeasures, it is known that turbulence which is caused by a rib portion to be formed in a base portion and a blade portion of a cooling fan when the cooling fan equipped in a rotor of the vehicle AC generator rotates is made to flow smoothly by deleting the rib portion (see, for example, Patent Document 1).
On the other hand, centrifugal force is acted on a blade by rotation. In this case, as a countermeasure against leaning after receiving force in an outer diameter direction, there is shown one in which a cutout provided on the inner circumferential side of a blade portion is devised so as to be in perpendicular to the radial direction of a claw (see, for example, Patent Document 2).
Particularly, in the case where it is compelled to set a low strength blade in which only a part of the fan blade is coped with a magnetic pole claw by adopting unequal pitches in consideration of order dispersion of fan sound, it can be coped with by forming a cutout having a length of 2.2 times or less in a dimension R at the root of the fan blade.